1. Field of the Invention
The present invention relates to a decompression mechanism for moderately reducing the compression pressure in a combustion chamber to thereby alleviate the operational load during the starting operation in an engine in which a cam for opening and closing an engine valve is integrally connected to one end face of a driven timing gear driven in a speed-reduced manner from a crankshaft. In particular the present invention is directed to an improvement in a decompression mechanism in an engine, including an annular recess defined in the other end face of the driven timing gear; a decompression cam shaft provided to extend from the annular recess to the cam and rotated between a first position in which a very small lift portion is formed on a base face of the cam and a second position in which the very small lift portion is retracted. A pivot is formed at the base end of a centrifugal weight accommodated in the annular recess, the pivot being fitted into a pivot bore provided in the driven timing gear. An operating pin is formed at the tip end of the centrifugal weight and engages the decompression cam shaft, so that the decompression cam shaft can be rotated from the first position to the second position by the centrifugal operation of the centrifugal weight. A decompression spring is connected to the centrifugal weight, for biasing the centrifugal weight toward the first position.
2. Description of the Prior Art
A decompression mechanism in the engine is already known, for example, as disclosed in Japanese Patent Publication No. 6-6889. In this decompression mechanism, the centrifugal weight is made of a steel plate, and the pivot and the operating pin are coupled to base and tip ends of the centrifugal weight by caulking or welding. Therefore, a number of parts are used and moreover, the manufacturing of the decompression mechanism is relatively troublesome, and it is difficult to reduce the cost.